Restriction fragment length polymorphism (RFLP) analysis was performed on a panel of 39 serologically typed DR homozygous monkeys. DNA was digested with the restriction enzyme TaqI and hybridizations were carried out with a human leukocyte antigen (HLA)-DR beta 3'UT-specific probe. In addition a panel of 18 monkeys was analyzed comprising experimental autoimmune encephalomyelitis (EAE) susceptible and nonsusceptible animals. The number of DRB/TaqI fragments detected for the various DR specificities varied from two to six, suggesting that the number of DRB genes per haplotype is not constant. RFLP typing allows that most serologically defined DR specificities can be subdivided. This knowledge was applied to define the DR specificities of the animals used for EAE experiments.